Using non-professional actors in a fictional movie is a high-risk business. There is a danger that they will, paradoxically, not look "real", or that they will look real and that their authenticity will somehow expose the fiction and createdness of the rest of the film. This blog is a footnote on this subject: in cinemas at this moment, there are two interesting uses of non-professionals.

In Joanna Hogg's Archipelago, the role of the artist and painting teacher Christopher is played by real-life artist Christopher Baker. His character, always laid-back and softly spoken, becomes a kind of father-figure to the troubled young Edward, played by Tom Hiddleston, as the pain caused by his absent father becomes ever clearer. It is a measure of how naturalistic Hogg has made her film and to the rest of the performers that Baker's gentle, amiable performance does not stand out too much. But I think it is recognisable as a non-professional's contribution.

The other example is Ken Loach's new film Route Irish, which comes out on Friday. It is a movie about which I have mixed feelings, but what is certainly notable about the film is its bold, almost workshop-ish use of non-professionals, mixed in with regular actors. Loach is well known for his interesting habit of using standup comics in his films in straight roles – which is a variant on "non-professional" casting. In Bread and Roses (2000), he used the Mexican-American standup George Lopez as the horrible office manager, and created one of the nastiest screen villains of the last decade. In The Navigators (2001), he used northern club comic Charlie Brown, as one of the railwaymen betrayed by privatisation. In Route Irish, Loach has cast John Bishop, the Liverpool standup star now on tour, in the role of an ex-soldier who goes back to work in Iraq as a private security contractor. It's an inspired choice – and Bishop carries off the role very well.

Route Irish has another interesting non-professional performance. Kurdish singer and musician Talib Rasool has a cameo, playing a version of himself as a musician who must pay the bills with his day job in IT and computers. He is approached by one character to recover incriminating video clips from a mobile phone, and to translate audible conversations into English, which will prove that security contractors are terrorising and killing Iraqi civilians. Rasool's performance is low-key, and he is never called upon to give a thespian performance. Yet his quiet disgust and outrage at what is on the mobile phone – and his lively suspicion that the person who brought it to him is somehow complicit in the abuse – is powerful: it almost looks as if Rasool is simply not acting, but genuinely considering the fact of abuse in the real world. The reality of Rasool's reactions, in that moment, somehow delivers more of a punch than a dozen thrillers.

Many people in the cinema prefer to watch professional actors. Archipelago and Route Irish, however, in their differing ways, show how effective non-professionals can be.